1. Application of differential staining techniques and continued improvement of established methods are basic to all of the projects conducted in the laboratory. 2. Human cytogenetic studies of patients with congenital and developmental disorders as well as studies of mutagen-induced chromosomal abnormalities are continuing. 3. Murine cytogentic studies include evaluation of mitotic and meiotic chromosomes and karyotypic evaluation of cells in hematopoetic tissue regeneration experiments. These are part of projects utilizing the mouse as a model for human diseases. 4. Study of the fate of oppisite sex syngeneic transfers in non-irradiated mice. 5. Study of sex changes in fish.